1. Field of Invention
The present invention relates to metallic sheet piles included as intermediate sections in combined supporting walls intended to hold back the soil, and more particularly, to a Z-shaped sheet pile with a high section modulus.
2. Description of the Related Art
Z-shaped sheet piles have been known for a long time. They have an inclined web connected to two substantially parallel flanges. Each flange is fitted with a gripping element, in order to form a joint in a supporting wall by interlocking with a gripping element of an adjacent sheet pile. In such a wall, the Z-shaped sheet piles are most frequently arranged constructed so that their flanges are substantially parallel and equidistant from the neutral bending plane of the wall. The product obtained by multiplying the section modulus of the wall with respect to this neutral plane by the maximum admissible elastic stress determines the maximum elastic moment that the wall can withstand.
What is called the "section modulus per unit length" of the sheet-pile wall is the section modulus with respect to the neutral plane of the wall per running meter of the wall. What is called the "specific section modulus" or the "performance criterion" of the sheet-pile wall is the section modulus per unit length divided by the mass of the wall per square meter of wall. It is specified that a "sheet-pile wall" in the present context is understood to be a wall consisting of Z-shaped sheet piles which are connected so that their flanges are substantially parallel and equidistant from the neutral bending plane of the wall.
ProfilARBED S.A. (Luxembourg) currently market a Z-shaped sheet pile called "AZ36", which has a section modulus of 3600 cm3 per running meter of wall. This AZ36 sheet pile has a mass of 194 kg/m2 and hence a specific section modulus of 18.6 (cm3/m)/(kg/m2). This is a sheet pile with gripping elements of the LARSSEN type shown in FIG. 1 as elements 20', 20", which are well known in the field, and with a web making an acute angle of about 63.degree. with a plane parallel to the flanges. ProfilARBED S.A. (Luxembourg) also market a Z-shaped sheet pile called "BZ42", which has a section modulus of 4200 cm3 per running meter of wall, but a mass of 271 kg/m2 and hence a less favorable specific section modulus of 15.5 (cm3/m)/(kg/m2). This is a sheet pile with gripping elements of the BELVAL type and with a web making an acute angle of about 83.5.degree. with a plane parallel to the flanges. Other types of Z-shaped sheet piles also to be found on the market can have section modulus up to 4550 cm3 per running meter of wall. However, these types of sheet pile with a higher section modulus are very heavy sections, with a very great weight per square meter of wall and therefore quite a low specific section modulus. Now, the lower the specific section modulus the higher the cost price of the wall.
The main reasons why Z-shaped sheet piles with a section modulus greater than 4550 cm3 are not found on the market are as follows:
Most frequently, there is a limit to the maximum thickness of the flanges. This is because the rolling of the gripping elements, particularly the LARSSEN type gripping elements, requires the flanges to be folded during the last pass of the rolling mill. Now, this folding becomes very difficult when the thickness of the flanges becomes too large. Thus, there is no present industrial method of rolling flanges with a thickness greater than 20 mm when they have gripping elements of the LARSSEN type. PA1 There is also a limit on the maximum width of the flanges and the maximum distance between the outer faces of the flanges (height of the section). This is because, for a given angle of inclination of the web, the width of the flanges and the height of the section determine the development of the sheet pile and PA1 A saving in the rolling width could be achieved by increasing the acute angle that the web makes with a plane parallel to the flanges (angle of inclination of the web). However, the nearer this angle of inclination of the web is to 90.degree. the greater the resistance experienced when driving in the sheet pile. For reasons related to the use of the sheet pile, it is therefore recommended that the angle of inclination of the web should be chosen to be less than 75.degree..
consequently the width of the roll stand rollers. Now the width of these rollers is limited by the width of the roll stands of the sheet pile rolling train. If it is required to roll sheet piles with a high section modulus on current rolling PA2 trains, the development of these sheet piles between the axes of the gripping elements must be less than a value predetermined by the width of the roll stands of the sheet pile rolling train.
Using an optimization program and a computer, the above-mentioned parameters have been optimized for a type AZ sheet pile, and a sheet pile has been obtained with a maximum section modulus of 4400 cm3 per running meter of wall. This type AZ sheet pile has, for a web thickness of 15 mm, a mass of 229 kg/m2 and thus a specific section modulus of 19.21 (cm3/m)/(kg/m2). A section modulus of 4400 cm3 therefore seems to be a limiting value for a Z-shaped sheet pile when compliance with the above-mentioned constraints is required. It would of course be possible to increase the web thickness still further, but such a step, while slightly increasing the section modulus, would mainly cause an appreciable reduction in the specific section modulus of the sheet pile.
The problem on which the present invention is based is to find a solution in order to increase still further the section modulus of a hot-rolled Z-shaped sheet pile, without at the same time reducing the specific section modulus of the sheet pile and without requiring an increase in the width of the roll stands.
This problem finds a solution in a Z-shaped sheet pile according to the first claim.
As regards the present state of the art, it should also be noted that the protruding extensions at the points connecting the flanges and webs of the sheet piles have already been described in the documents U.S. Pat. No. 1,831,427 and FR-A-686816, but are so described in a context completely different from the present invention. In fact, neither of these two documents relates to hot rolling or to the increase in the section modulus of a Z-shaped sheet pile. The document U.S. Pat. No. 1,831,427 describes special Z-shaped sheet piles which make it possible to produce, in cooperation with intermediate flat sheets, a sheet-pile wall with a continuous plane surface. The special sheet piles described in this document are more than likely sheet piles made of cast iron. Their web makes an angle close to 90.degree. with a plane parallel to the outer faces of the flanges. At the joins between the web and the flanges, they have ribs, ridges, shoulders or projections incorporated in the sheet pile or attached by any means whatsoever to it. The only purpose of these ribs, ridges, shoulders or projections is to become engaged in recesses of complementary shape made in the said intermediate sheets. In this way, they make it possible to insert and hold in place these intermediate sheets between two Z-shaped sheet piles, in order to create the sheet-pile wall with a continuous plane surface. U-shaped sheet piles of small height are known from the document FR-A-686816, such sheet piles having a reinforced part at the position of the connections between the web and the flanges. In an assembly consisting of two of these sheet piles, the said reinforced part, located immediately before the opening in a clutch in the first sheet pile, acts in combination with the inner part of this clutch to create a shape capable of cooperating with the outer part of a clutch on the second sheet pile.
The hot-rolled Z-shaped sheet pile according to the invention comprises, like all hot- rolled Z-shaped sheet piles, two flanges having substantially parallel outer faces, and an oblique web connected to the two flanges. This web makes an acute angle less than or equal to 75.degree. with a plane parallel to the outer faces of the flanges and is delimited between the connections to the flanges by two substantially plane faces. The hot-rolled sheet pile according to the invention is distinguished from a conventional hot-rolled sheet pile mainly in that each of the two flanges has an extension which protrudes with respect to a fictional plane extending the plane face of the web located on the same side as the outer face of the respective flange.
It is to be appreciated that a hot-rolled sheet pile according to the invention has the advantage of being produced with a small surplus of material, and therefore with a small increase in the mass per square meter of wall, a distinct improvement in the section modulus and consequently also an improvement in the specific section modulus. It is to be particularly appreciated that this improvement in the section modulus may be obtained without increasing the width of the roll stands, without increasing the thickness of the flanges, and that it even makes it possible to increase the useful width of the flanges. The proposed solution also leads to a strengthening of the corners of the flange/web connection on the outer side, and hence a lower risk of these critical places being damaged when the sheet piles are used. This strengthening is also favorable to a better resistance to accelerated corrosion at low water levels since Z-shaped sheet piles, unlike U-shaped sheet piles, have above all a tendency to become corroded at the web/flange connections. It remains to point out that the flanges have greater supporting surfaces (=outer faces of the flanges) for walling or anchoring plates, and that the transmission of the anchoring forces from the flanges to the web and vice versa is improved.
It is to be particularly appreciated that it has been possible to obtain sheet piles according to the invention with the following characteristics:
______________________________________ thickness of flanges approximately 19 to 20 mm; width of flanges 200 mm; height of sheet pile 500 mm; section modulus per unit length 4800 cm3/m; of wall specific section modulus approximately 20 (cm3/m)/(kg/m2). ______________________________________